The effect of organic load and feed strategy on biohydrogen production in an AnSBBR treating glycerin-based wastewater

Thermophilic and mesophilic anaerobic digestion of soybean molasses: A performance vs. stability trade-off

One of the factors that has a direct impact on anaerobic digestion is the applied organic loading rate (OLRA). Increasing OLRA can boost methane production but can also cause process failure. As a result, establishing the appropriate OLRA for the procedure is critical. This study evaluated the effect of increasing the OLRA using soybean molasses in a thermophilic anaerobic reactor (R-Thermo), as well as the effect of feeding strategy and co-processing with okara. Furthermore, the performance versus stability trade-off between R-Thermo and mesophilic anaerobic digestion (R-Meso) was investigated. The increase of OLRA from 10 to 15 and 20 kg-COD/m³/d led to a decrease in COD removal efficiency (90, 86, and 75%), methane yield (12.0, 11.6, and 9.9 mol-CH4/kg-COD) and an increase in total volatile acids concentration (251, 456, and 1393 mg-HAc/L, respectively). At 15 kg-COD/m³/d, R-Meso performed similarly to R-Thermo, and at 20 kg-COD/m3/d, R-Meso outperformed (81% COD removal efficiency, 9.3 mol-CH4/kg-CODrem and 154.5 mol-CH4/m3/d). Temperature greatly influenced the distribution of metabolic pathways, as shown by thermodynamic and kinetic analyses, thus impacting bacterial diversity. At 55 °C, amongst the bacterial genera, Tepidiphilus stood out (>28.2%), followed by Acetomicrobium, Coprothermobacter and Candidatus_Caldatribacterium. The OLRA clearly impacted the archaeal community; Methanothermobacter (77.4%) was favored over Methanosarcina (14.8%). Under thermophilic temperature, it seems that syntrophic acetate oxidation (SAO) bacteria might have competed for substrate with acetoclastic methanogens, while in R-Meso microorganisms responsible for the initial steps of organic matter breakdown, such as members of the Firmicutes and Proteobacteria phyla (at least 67%), were dominant. In summary, R-Meso, characterized by a more uniform distribution of metabolic pathways, as well as a diverse and well-adapted microbial consortium, have exhibited enhanced stability and outperformed R-Thermo at high-loads.

Integrated production of hydrogen and methane in a dairy biorefinery using anaerobic digestion: Scale-up, economic and risk analyses

Anaerobic digestion has emerged as the most appealing waste management strategy in biorefineries. Particularly, recent studies have highlighted the energy advantages of waste co-digestion in industrial biorefineries and the use of two-stage systems. However, there are some concerns about moving the system from laboratory testing to industrial scale. One of them is the high level of investment that is required. Therefore, this study carried out a techno-economic analysis (scale-up and energy production, economic and risk analysis, and factorial design) to assess the feasibility of single- and two-stage systems in the treatment of cheese whey and glycerin for the production of hydrogen and methane. Scenarios (S1 to S9) considered thermophilic and mesophilic single and two-stage systems with different applied organic loading rates (OLRA). The analyses of scale-up and energy production revealed that S3 (a thermophilic single-stage system operated at high OLRA 17.3 kg-COD.m-3.d-1) and S9 (a thermophilic-mesophilic two-stage system operated at high OLRA 134.8 kg-COD.m-3.d-1 and 20.5 kg-COD.m-3.d-1, respectively) were more compact and required lower initial investment compared to other scenarios. The risk analysis performed by a Monte Carlo simulation showed low investment risks (10 and 11%) for S3 and S9, respectively, being the electricity sales price, the key determining factor to define whether the project in the baseline scenario will result in profit or loss. Lastly, the factorial design revealed that while the net present value (NPV) is positively impacted by rising inflation and electricity sales price, it is negatively impacted by rising capitalization rate. Such assessments assist in making decisions regarding which system can be fully implemented, the best market circumstances for the investment, and how market changes may favorably or unfavorably affect the NPV and the internal rate of return (IRR).

Performance of an anaerobic sequencing batch reactor operating under high organic loading in treatment of biodiesel wastewater

Studies reporting the performance of anaerobic sequencing batch reactor (AnSBR) operating with high organic loadings are scarce. This study aimed to contribute to the technical and scientific literature by reporting the experience obtained when biodiesel wastewater was treated in an AnSBR applying organic loading rates (OLR) above those commonly used in batch reactor projects. For this, physicochemical and chromatographic analysis of the effluent were carried out. Further, the biomass was assessed chemically and morphologically, along with bacterial diversity characteristics. Supported by these analyses, the system performance was discussed in terms of COD remotion efficiency and buffering capacity. The AnSBR reached 10% of COD removal at the steady-state, which caused the biomass defragmentation and facilitated washout. This suggests that the startup and operation of AnSBR under optimized conditions with an average applied OLR of 11.3 gCOD L-1 d-1 worked as a pressure for the microbiota selection, stimulating the production of total volatile acids, which promoted system reduction efficiency and souring. In this context, food/microorganism ratios above 1.0 gCOD gTVS -1 d-1 can favor acidogenic activity, and total volatile acids/bicarbonate alkalinity concentration ratios above 1.9 may indicate acidification. The addition of support material for immobilizing/increasing biomass retention and/or operation under two-stage may be interesting alternatives for increasing AnSBR efficiencies under high OLRs.

Graphical abstract

Effect of the Progressive Increase of Organic Loading Rate in an Anaerobic Sequencing Batch Reactor for Biodiesel Wastewater Treatment

The wastewater from the biodiesel industry is an environmental problem, and from a sanitation resources perspective, the anaerobic sequencing batch reactor (ASBR) is an interesting alternative for wastewater treatment. A better understanding of ASBR operation behavior under the progressive increase of the organic loading rate (OLR) is crucial for upscaling. The objective of this study was to monitor an ASBR operating with an OLR ranging from 1.3 to 9.3 kgCOD m−3 d−1. The average chemical oxygen demand (COD) removal efficiencies of the ASBR were 52, 41, 47, and 11% for phases 1, 2, 3, and 4, respectively. The apparent kinetic coefficient, i.e., the rate of degradation of organic matter, was between 0.10 and 1.80 h−1, considering the kinetic model that considers the residual substrate concentration, which was the one that best fit the obtained data. The progressive increase in applied OLR modified the microbial biomass diversity, which in turn influenced the degradation kinetics of the organic matter. In addition, the values of the applied OLR of 5.1 kgCOD m−3 d−1 and a food to microorganism ratio (F/M) of 0.6 kgCOD kgVSS−1 d−1 were shown to be limiting values that promoted the overload of ASBR.

S/X ratio impacts the profile and kinetics of carboxylic acids production from the acidogenic fermentation of dairy wastewater

The acidogenic fermentation of dairy wastewater (DW) was evaluated for carboxylic acids (CA) production, investigating the influence of substrate/microorganism (S/X) ratio and applying different mathematical models to the bioproduct formation data. The experiments were performed in batch reactors for 28 days, and four S/X ratios were tested (0.8, 1.2, 1.6, and 1.9 gCOD gVSS^-1). The S/X ratio increase did not influence the percentage of DW conversion into carboxylic acids (42-44%), but the productivity was positively affected (100-200% in general). Acetic acid was the CA formed in the highest concentration for all experiments, followed by propionic and butyric acids. Exponential models were better suited to describe this kinetics process. Therefore, according to the estimated kinetic parameters, the S/X ratio 1.6 was more suitable for CA production from acidogenic fermentation of dairy wastewater, in which the concentrations of longer CA, such as propionate and butyrate, were formed in higher quantities. In addition, it was determined a correlation between the S/X ratio and kinetic parameters like degradation/production rate constant (K) and maximum productivity rate (μ_m).

One waste and two products: choosing the best operational temperature and hydraulic retention time to recover hydrogen or 1,3-propanediol from glycerol fermentation

This study aimed to compare the production of hydrogen and 1,3-propanediol from crude glycerol (10 g/L) in mesophilic (30 °C) and thermophilic (55 °C) anaerobic fluidized bed reactors, namely AFBR_30 °C and AFBR_55 °C, respectively, at hydraulic retention times (HRT) reduced from 8 to 1 h. In AFBR_30 °C, the absence or low hydrogen yields can be attributed to the production of 1,3-propanediol (maximum of 651 mmol/mol glycerol), and the formation of caproic acid (maximum of 1097 mg/L) at HRTs between 8 and 2 h. In AFBR_55 °C, the hydrogen yield of 1.20 mol H₂/mol glycerol consumed was observed at the HRT of 1 h. The maximum yield of 1,3-propanediol in AFBR_55 °C was equal to 804 mmol/mol glycerol at the HRT of 6 h and was concomitant with the production of hydrogen (0.87 mol H₂/mol glycerol consumed) and butyric acid (1447 mg/L).